The research broadly deals with the subject of IgA proteases, enzymes produced by pathogenic microorganisms that have human immunoglobulin IgA as their only substrate. Neisseria gonorrhoeae, N, meningitidis and streptococcus sanguis species are enzyme-positive. The secretory immune system in man is mediated largely by antibody of the IgA isotype, this ss the form of Ig susceptible to proteolysis by the enzymes. The peptide bond in the IgA heavy chain cleaved by each enzyme has been identified. No other substrates have been found IgA protease-susceptible. Our research now will concern itself with studying the membranes of bacteria for the presence of enzyme, as S. sanguis organisms themselves are IgA-protease positive after extensive washing. Also, because secretory IgA inhibits IgA protease activity, we are exploring the possibility that this inhibition represents an antibody response to the enzyme protein by the secretory immune apparatus. Third, we are collaborating with other laboratories in work to identify the precise location of secretory component covalent bonding on the secretory IgA heavy chain. In summary, the research on IgA proteases is an attempt to understand the subtle interaction between microbial pathogens and the elements of secretory immunity which we involved in defense of mucosal surfaces.